Workday rises after Elliott backs leadership, builds more than $2 billion stake

** Shares of human resources software provider Workday WDAY.O rise nearly 9% to $237 in early trading

** Activist investor Elliott Management builds more than $2 billion stake in WDAY and voices support for company's leadership

** Company on Tuesday announced it would buy AI firm Sana for about $1.1 bln

** This is WDAY's third AI-related deal in less than two months, following the acquisition of Paradox and Flowise in August

** Workday shares down 15% YTD